Method for fabricating quartz-based nanoresonators

ABSTRACT

A method for fabricating a quartz nanoresonator which can be integrated on a substrate, along with other electronics is disclosed. In this method a quartz substrate is bonded to a base substrate. The quartz substrate is metallized so that a bias voltage is applied to the resonator, thereby causing the quartz substrate to resonate at resonant frequency greater than 100 MHz. The quartz substrate can then be used to drive other electrical elements with a frequency equal to its resonant frequency. The quartz substrate also contains tuning pads to adjust the resonant frequency of the resonator. Additionally, a method for accurately thinning a quartz substrate of the resonator is provided. The method allows the thickness of the quartz substrate to be monitored while the quartz substrate is simultaneously thinned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. applicationSer. No. 11/043,378, filed on Jan. 25, 2005, now U.S. Pat. No. 7,459,099which is a division of U.S. Non-Provisional patent application Ser. No.10/426,931 filed on Apr. 30, 2003, now U.S. Pat. No. 7,237,315 whichapplication is related to and claims the benefit of U.S. ProvisionalApplication No. 60/376,995, filed Apr. 30, 2002, the contents of whichare incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein was made under a government contract withthe Defense Advanced Research Projects Agency (DARPA), NMASP program,contract #DAAB07-02-C-P613.

FIELD

The present invention relates to a method for making a resonator. Morespecifically, the present invention relates to a method for fabricatingnanoresonators using a quartz substrate integrated with a basesubstrate, and a method for thinning the quartz substrate.

BACKGROUND

The use of quartz substrates in a MEMS process provides for thefabrication of high Q, thermally compensated resonators. For thicknessshear mode resonators, the thickness of the substrate determines itsresonant frequency. The thinner the quartz substrate, the higher theresonant frequency. Therefore, by varying the dimensions of thesubstrate over a broad range, the resonant frequency can be adjustedover a broad range. The Q of a resonator is a measure of the frequencyselectivity of a resonator and is related to how well the energy of theoscillations are trapped. One factor that influences how well the energyof the oscillations is trapped is the smoothness of the surface. Whenthinning a quartz substrate it is desirable to maintain a smoothundamaged surface to ensure a high Q. However, present quartzfabrication techniques for oscillators or filters do not allow theresonators to be integrated on a chip with other electronics. This is asignificant contributing factor to the size and cost of a device. Usingseparate on chip components also contributes significantly to the sizeand cost of a device.

Furthermore, present quartz thinning processes have not be able to thinsubstrates to a thickness on the order of 10 micrometers or less,because of the inability to monitor the thickness of the quartzsubstrate in real time with sub micron resolution. Another difficulty isthe handling of the quartz substrate after it has been thinned. Onereference which discusses thinning quartz substrates is Takahsi Abe,Masayoshi, “One-Chip Multichannel Quartz crystal microbalance (QCM)Fabricated By Deep RIE,” Sensors and Actuators, 2000, pp. 139-143.Having a quartz substrate with a thickness on the order of 10 microns orless can result in resonant frequencies greater than 100 MHz, which isdesirable for high frequency applications. By combining several quartzbased resonators having different resonant frequency, with a RF MEMSswitch on the same chip, frequency hopping and filter reconfigurationcan occur on the microsecond time scale. In frequency hopping and filterreconfiguration the desired frequency in a band of frequencies isselected by using the RF MEMS switch to activate the quartz resonatorhaving a resonant frequency equal to the desired frequency. The spectralband for most radio frequency hopping and filter reconfigurationapplications is 20 MHz to 3 GHz. The low frequency part of the band isextremely difficult to cover with conventional capacitive-based filterssince capacitive-based filters are larger in size. Frequency hopping andfilter reconfiguration applications would also benefit from temperaturecompensated, stable, high-Q (in the amount of about 10,000), smallarrays of resonators which cover that spectral band.

MEMS devices which consist of silicon-based nanoresonators have beenfabricated in an attempt to integrate nanoresonators or microresonatorswith other electronics. Nanoresonators and microresonators areresonators which have linear dimensions on the order of nanometers andmicrometers, respectively. These silicon-based nanoresonators have shownresonant frequencies as high as 600 MHz, and Q's in the range of1000-2000. However, the problem with silicon-based nanoresonators isthat they have high electrical impedances and lower Q's. Two documentswhich discuss silicon-based nanoresonators are S. Evoy, A. Olkhovets, L.Sekaric, J. M. Parpia, H. G. Craighead, D. W. Carr,“Temperature-dependent Internal Friction in SiliconNanoelectromechanical Systems,” Applied Physics Letters, Vol. 77, Number15, and A. N. Cleland, M. L. Roukes, “Fabrication of High FrequencyNanometer Scale Mechanical Resonators From Bulk Si Crystals,” AppliedPhysics Letters, Oct. 28, 1996.

An alternative solution, is known which makes use of non-MEMS quartzresonators. Such resonators consist of shear strip individual resonatorsoperating in ranges of about 10 MHz to about 1 GHz. These resonators arepackaged as discrete devices and mounted as hybrids to other RFcircuits. The problem with non-MEMS quartz resonators is that they arenon-integrable, they have higher costs, and they are physically largerin size.

As a result, a new process for manufacturing a quartz-basednanoresonator is desired in order to solve all the aforementionedproblems.

SUMMARY

The present invention describes a method for fabricating and integratingquartz-based resonators on a high speed substrate for integrated signalprocessing by utilizing a combination of novel bonding and etching stepsto form ultra thin quartz based resonators. Thinning the quartzsubstrate in the quartz resonator can be used to provide the desiredresonant frequency and may be in excess of 100 MHz.

According to one aspect of the present invention, a novel method forfabricating a quartz based resonator is disclosed. The method makes useof the bond between the quartz substrate and the silicon substrate, aswell as a novel process to thin the quartz substrate to a desiredthickness. A quartz substrate is provided having a first electrodedeposited thereon. The quartz substrate is bonded to a first substratehaving a cavity etched therein to accommodate the first electrode. Thequartz substrate is then thinned to a desired thickness and a secondelectrode is deposited on the quartz substrate. The first electrode isconnected to the second electrode with vias which are filled with ametal. In addition to the first and second electrodes, a tuning pad ispreferably deposited on the quartz substrate. Further, the presentinvention provides a base substrate which contains probe pads. Afterdepositing the first and second electrodes and the tuning pads on thequartz substrate, the probe pads of the base substrate are bonded to thesecond electrodes of the quartz substrate. The tuning pad can be used toadjust the resonant frequency of the quartz substrate. Further, it isalso possible to use the first and second electrodes as tuning pads.More specifically, the first and second electrodes may be ablated toadjust the resonant frequency of the nanoresonator. Additionally, thebase wafer could contain high-speed RF electronics, which would suppressthe need for lengthy bond wires. The first substrate is then removedfrom the quartz substrate thereby releasing the resonator.

It is also an object of the present invention to provide a method forfabricating a quartz based resonator without the use of a silicon wafer.In this embodiment first electrodes and a tuning pad are deposited onthe quartz resonator. A base substrate is also provided. The basesubstrate contains probe pads for providing an electrical connection tothe quartz substrate. The quartz substrate is bonded to the basesubstrate and then undergoes a thinning process. After the quartzsubstrate is thinned, second electrodes and a tuning pad are depositedon the quartz substrate.

It is also an object of the present invention to provide a novel methodfor thinning a quartz substrate. In this method, a lap and polish systemis used to remove a substantial portion of the quartz substrate. Thenreactive ion etching is used thin the quartz substrate to a thicknessless than 10 micrometers, which is needed for resonant frequenciesgreater than 100 MHz. The reactive ion etching is used simultaneouslywith an optical monitoring technique to obtain the current thickness ofthe quartz substrate as it is being thinned. After obtaining the desiredthickness of the quartz substrate using reactive ion etching, the quartzsubstrate can be further polished using a chemical mechanical polish(CMP) or a wet etch.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 shows a quartz substrate, silicon substrate and base substrate,to be used in accordance with a first embodiment of the presentinvention;

FIG. 2 shows the silicon substrate with a cavity;

FIG. 3 shows photoresist on the quartz substrate;

FIG. 4 shows the quartz substrate with first electrodes and a tuningpad;

FIG. 5 a shows the quartz substrate bonded to the silicon substrate;

FIGS. 5 b-5 e show the thinning of the quartz substrate while bonded tothe silicon substrate;

FIGS. 6 a and 6 b show two methods used to monitor the thickness of thequartz substrate while being thinned;

FIG. 7 shows vias in the quartz substrate;

FIG. 8 shows the same as FIG. 7 except second electrodes and a tuningpad have been deposited on the quartz substrate;

FIG. 9 shows the same as FIG. 8 except a portion of the quartz substratehas been removed;

FIG. 10 shows a portion of the base substrate having been removed;

FIG. 11 shows the same as FIG. 10 except probe pads have been added tothe base substrate;

FIG. 12 shows the bond between the probe pads of the base substrate andthe second electrodes on the quartz substrate; and

FIG. 13 shows the same as FIG. 12 except the silicon substrate has beenremoved.

FIG. 14 shows the quartz substrate and base substrate to be used inaccordance with a second embodiment of the present invention;

FIG. 15 shows the quartz substrate with first electrodes and a tuningpad;

FIG. 16 shows a portion of the base substrate having been removed;

FIG. 17 shows the same as FIG. 16 except probe pads have been added tothe base substrate;

FIG. 18 shows the quartz substrate bonded to the base substrate;

FIG. 19 shows the thinning of the quartz substrate while bonded to thebase substrate;

FIG. 20 shows the vias created in the quartz substrate;

FIG. 21 shows the second electrodes and tuning pad on the quartzsubstrate; and

FIG. 22 shows the same as FIG. 21 except a portion of the quartzsubstrate removed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a method for fabricating a resonator withreference to FIGS. 1-22.

First Embodiment

A method of fabricating a quartz resonator according to a firstembodiment of the present invention will now be described with referenceto FIGS. 1-13. Referring to FIG. 1, a quartz substrate 2 having a firstsurface 3 and a second surface 5, a first substrate 4, and a basesubstrate 14 are provided. The first substrate 4 may comprise a materialsuch as silicon or GaAs. In this embodiment, both the first substrate 4and quartz substrate 2 may be provided in the form of 3 inch or largerwafers. A portion of the first substrate 4 is etched away creating acavity 6, as shown in FIG. 2. The etched cavity 6 can be fabricated witha wet etch of potassium hydroxide, or a dry reactive ion etch using agas having a fluorine chemistry.

The first surface 3 of the quartz substrate 2 is then patterned andmetallized using a lift-off technique. In the lift-off technique, a thinlayer of photoresist 7 is patterned on the first surface 3 of the quartzsubstrate 2, as shown in FIG. 3. Using lithography, photoresist isremoved in the regions where metallization is desired. The metal is thendeposited on the photoresist 7 and in the regions where the photoresist7 was removed. The photoresist is then removed leaving metal only in thedesired regions on the first surface 3 of the quartz substrate 2 asshown in FIG. 4. During patterning and metallizing at least one firstelectrode 8 is deposited on the first surface 3 of the quartz substrate2. The first electrode 8 may be comprised of a combination of Ti, Pt,Au, or Cr, Pt, Au, deposited in that order on the first surface 3 of thequartz substrate 2 in that order. Shown in FIG. 4 are two firstelectrodes 8 on the first surface 3 of the quartz substrate 2.Additionally, a first tuning pad 10 may be deposited on the firstsurface 3 of the quartz substrate 2. The first tuning pad 10 iscomprised of the same material as the first electrodes 8. The purpose ofthe two first electrodes 8 and the first tuning pad 10 will be discussedlater.

After the first electrodes 8 and the first tuning pad 10 are deposited,the quartz substrate 2 is bonded to the etched first substrate 4, asshown in FIG. 5 a using for example, an EV 501 Wafer Bonder which iscommercially available. To bond the quartz substrate 2 to the firstsubstrate 4, the quartz substrate 2 and first substrate 4 are thoroughlycleaned in a megasonic cleaning system, which makes use of ultrasonicwaves to remove particle contaminants. After the wafers are cleaned,they are brought in contact with each other. The contact between thequartz substrate 2 and the first substrate 4 creates a bond due to thewell known van der Waals force. The first electrodes 8 and the firsttuning pad 10 are now located in the cavity 6 of the first substrate 4.

The second surface 5 of the quartz substrate 2 remains exposed, andundergoes a thinning process, shown in FIGS. 5 b-5 e. In order to thinthe quartz substrate 2, the following method is used. For exemplarypurposes only, the quartz substrate 2 has an initial thickness of 500micrometers. A first portion of the quartz substrate 2 is removed bythinning the quartz substrate from about 500 micrometers to 50micrometers as shown in FIG. 5 b using a mechanical lapping andpolishing system. Lapping and polishing systems are well known andcommercially available from manufacturers such as Logitech. In amechanical lapping and polishing system, a polishing head is spun at ahigh rate of speed. The lapping and polishing system also comprises anozzle for dispensing slurry on the quartz substrate 2. While spinning,the polishing head contacts the quartz substrate in the presence of theslurry, thereby evenly grinding away portions of the quartz substrate 2.The slurry may be comprised of chemicals such as aluminum oxide toremove quartz from the quartz substrate 2.

Next, a second portion of about 1 micrometer of quartz is removed fromthe quartz substrate 2, as shown in FIG. 5 c to ensure a smooth surface.This is done with the above described mechanical lapping and polishingsystem, except a softer chemical such as colloidal silica or ceriumoxide is used in the slurry to remove quartz from the quartz substrate2.

Next, a third portion of the quartz substrate 2 is removed to reduce thethickness of the quartz substrate 2 to less than 10 micrometers as shownin FIG. 5 d using reactive ion etching (RIE) with CF₄ or SF₆ gas 9, asshown in FIGS. 6 a-6 b. While being thinned in the RIE machine, thethickness of quartz substrate 2 is simultaneously monitored usingspectropic ellipsometry or reflectometry techniques, as shown in FIGS. 6a-6 b. In spectroscopic ellipsometry, shown in FIG. 6 a, a beam of whitelight 18 from a source 19 is shone onto the quartz substrate 2 at anangle of about 15° off horizontal. The white light has a knownpolarization. The reflected white light 20 off the quartz substrate 2will have a different polarization which is directly related to thethickness of the quartz substrate 2. A receiver 21 receives thereflected white light 20 and calculates the change in polarization. Thechange in polarization is directly proportional to the thickness of thequartz substrate 2. In reflectometry, shown in FIG. 6 b, a laser source22 shines light 23, with a known wavelength, onto the second surface 5of the quartz substrate 2 at an angle of 90° off horizontal as shown inFIG. 6 b. A first reflected beam 24 is reflected off the second surface5 of the quartz substrate 2. A portion of the incident light alsopenetrates through the quartz substrate 2. This creates a secondreflected beam 25 which is reflected off the first surface 3 backthrough the quartz substrate 2 and out the second surface 5. The firstreflected beam 24 and second reflected beam 25 are parallel to eachother and are received by a receiver 26 which determines whether thefirst reflected beam 24 and the second reflected beam 25 addconstructively or destructively. If the first and second reflected beams24, 25 add constructively, the thickness of the quartz substrate isequal to 25% of the ratio of the incident light wavelength divided bythe refractive index of quartz, or an odd integer multiple thereof, suchas 75%, 125%, etc. The refractive index of quartz is typically about1.46. If the first and second reflected beams 24, 25 add destructively,the thickness of the quartz substrate 2 is equal to 50% of the ratio ofthe incident light wavelength divided by the refractive index of quartz,or an integer multiple thereof, such as 100%, 150%, etc.

After using RIE to remove quartz from the quartz substrate 2, thesurface of the quartz substrate 2 may have imperfections that need to becorrected. This can done by using the mechanical lapping and polishingsystem described above with a chemical such as silica or cerium oxide,to remove about 0.01-0.02 micrometers of quartz, followed up with a wetetch in ammonium bifluoride to remove about 0.005 micrometers of quartzfrom the quartz substrate 2, as shown in FIG. 5 e. This additional stepwill help ensure a polished, defect free quartz substrate 2.

After the quartz substrate 2 is thinned, vias 11 are fabricated in thequartz substrate 2, as shown in FIG. 7. The vias 11 are created usinglithography techniques well known in the art. The vias 11 are contactswhich are etched through the quartz substrate 2 to the first electrodes8. FIG. 7 shows two vias 11. Once the vias 11 are fabricated, the viasare metallized and the second surface 5 of the quartz substrate 2 ispatterned and metallized, as shown in FIG. 8, using the lift-offtechnique described for depositing the at least one first electrode 8.During the metallization step, at least one second electrode 12 isdeposited on the second surface 5 over the vias 11. The second electrode12 may be comprised of a combination of Ti, Pt, Au, or Cr, Pt, Au,deposited in that order on the second surface 5 of the quartz substrate2 in that order. Shown in FIG. 8 are two second electrodes 12.

The first and second electrodes 8, 12 are now connected through the vias11. Additionally, a second tuning pad 13 can be deposited during thestep of depositing the second electrodes 12, as shown in FIG. 8. Thesecond tuning pad 13 is comprised of the same material as the secondelectrodes 12. Once the first and second electrodes 8, 12 and first andsecond tuning pads 10, 13 have been deposited, a portion of the quartzsubstrate 2 is removed, thereby creating a modified quartz substrate 2a, as shown in FIG. 9. Such portion is removed using lithography and REItechniques well known in the art to divide the quartz substrate intoindividual devices and determine the desired dimensions of the quartzsubstrate 2.

The first and second tuning pads 10, 13 on the modified quartz substrate2 a allow the resonant frequency of the quartz substrate 2 a to beadjusted. By ablating a portion of the first and second tuning pads 10,13, the resonant frequency of the quartz substrate 2 a can be adjusted.However, it is also possible to adjust the resonant frequency byablating a portion of the first and second electrodes 8, 12. The firstand second tuning pads 10, 13 can be ablated using known techniques suchas focused ion beam milling or laser ablation.

As already mentioned above with reference to the detailed description ofFIG. 1, a base substrate 14 is provided. The base substrate 14 iscomprised of a group III-V material or SiGe. FIG. 10 shows a modifiedbase substrate 14 a, where a portion of the base substrate 14 shown inFIG. 1 has been removed. The removal of a portion of the base substrate14 is done using lithography techniques well known in the art. At leastone probe pad 16 is deposited on the modified base substrate 14 a. FIG.11 shows, for example, two probe pads 16. The probe pads are depositedusing the same lift off technique used to deposit the at least one firstelectrode 8 discussed previously. The probe pads 16 may be comprised ofa gold/germanium alloy, nickel, and gold deposited in that order.

After the probe pads 16 have been deposited on the modified basesubstrate 14 a, the bottom electrodes 12 of the modified quartzsubstrate 2 a are bonded to the probe pads 16 along bonding line 17, asshown in FIG. 12 using an Au—Au compression bonding scheme. In the Au—Aucompression bonding scheme, the quartz substrate 2, the secondelectrodes 12, the probe pads 16, and the modified base substrate 14 aare heated to a temperature greater than 300° C. in a vacuum having apressure no greater than 10⁻⁴ Torr. Then the second electrodes 12 andprobe pads 16 are pressed together, while depressurized, with a pressureof approximately 1 MPa. This will fuse the probe pads 16 and the secondelectrodes 12 together, as shown in FIG. 12.

The above described bonded structure provides electrical access from theprobe pads 16 to the first electrodes 8. After the second electrodes 12have been bonded to the probe pads 16, the quartz substrate 2 a isremoved from the remaining structure, using a combination of wet and dryetches so that a structure like the one shown in FIG. 13 is obtained.

The purpose of the first and second electrodes 8, 12 is to receive anelectrical signal from the probe pads 16 which can bias or drive themodified quartz substrate 2 a with an electric field. The electricalsignal is preferably an AC signal. When the electrical signal isreceived by the first and second electrodes 8, 12 a strain is placed onthe modified quartz substrate 2 a. This strain stimulates the mechanicalresonant frequency of the modified quartz substrate 2 a by thewell-known piezoelectric effect, thereby causing the modified quartzsubstrate 2 a to oscillate at its resonant frequency. Additionally, itis also possible to use the first and second electrodes 8, 12 to sensethe movement of the modified quartz substrate 2 a relative to aspecified plane (not shown). Once the modified quartz substrate 2 a isoscillating at its resonant frequency, it can be used to drive othercomponents at a frequency equal to its resonant frequency.

Second Embodiment

A second embodiment of a method for fabricating a quartz resonator willnow be described with reference to FIGS. 14-22. This second embodimentis similar to the first embodiment, except the first substrate isremoved from the process. In this embodiment, a quartz substrate 30 anda base substrate 40 are provided, as shown in FIG. 14. A first surface31 of the quartz substrate 30 is patterned and metallized using thelift-off technique discussed in the first embodiment for depositingfirst electrodes 8. During patterning and metallizing, at least onefirst electrode 36 is deposited on the first surface 31 of the quartzsubstrate 30. FIG. 15 shows two first electrodes 36. Additionally, afirst tuning pad 38 is deposited on the first surface 31 of the quartzsubstrate 30.

As aforementioned, a base substrate 40 is provided. This base substrate40 is comprised of a group III-V material or SiGe. In order to obtain amodified base structure 40 a, shown in FIG. 16, a portion of the basestructure 40 is removed using the techniques discussed in the firstembodiment. At least one probe pad 42 is deposited on the modified basesubstrate 40 a using the lift-off technique discussed in the firstembodiment for depositing probe pads 16. Shown in FIG. 17 are two probepads 42.

After the probe pads 42 have been deposited on the modified basesubstrate 40 a, the first electrodes 36 of the quartz substrate 30 arebonded to the probe pads 42 along bonding line 43, as shown in FIG. 18using the Au—Au bonding scheme discussed in the first embodiment.

Next, the quartz substrate 30 is thinned to a thickness of 10micrometers or less, as shown in FIG. 19, using the technique discussedin the first embodiment. Vias 39 are fabricated in the quartz substrate30 using the techniques discussed in the first embodiment. The vias 39,shown in FIG. 20, are contacts which are etched through the quartzsubstrate 30 to the first electrodes 36. Once the vias 39 arefabricated, the vias 39 are metallized and the second surface 33 of thequartz substrate 30 is patterned and metallized using the lift-offtechnique discussed in the first embodiment for depositing secondelectrodes 12. During the metallization step, at least one secondelectrode 46 is deposited on the second surface 33 over the vias 39.Shown in FIG. 21 are two second electrodes 46. The first and secondelectrodes 36, 46 are connected through the vias 39. Furthermore, asecond tuning pad 48 can be deposited as shown in FIG. 21, duringpatterning and metallization of the second electrodes 46. Finally aportion of the quartz substrate 30 is removed, thereby creating amodified quartz substrate 30 a, as shown in FIG. 22, using lithographyand RIE techniques known in the art. Once the modified quartz substrate30 a is oscillating at its resonant frequency, it can be used to driveother components at a frequency equal to its resonant frequency.

Let it be understood that the foregoing description is only illustrativeof the invention. Various alternatives and modifications can be devisedby those skilled in the art without departing from the spirit of theinvention. Accordingly, the present invention is intended to embrace allsuch alternatives, modifications, and variances which fall within thescope of the appended claims.

1. A method for fabricating a resonator comprising the steps of:providing a first substrate having a cavity etched therein; providing aquartz substrate; bonding the quartz substrate to the first substrateand over the cavity; thinning the quartz substrate while opticallymonitoring a thickness of the quartz substrate; removing a portion ofthe thinned quartz substrate; bonding the thinned quartz substrate to abase substrate; and removing the first substrate from the thinned quartzsubstrate, thereby releasing the thinned quartz substrate from thethinned quartz substrate.
 2. The method of claim 1, wherein the step ofthinning the quartz substrate thins the quartz substrate to a thicknessof less than ten micrometers.
 3. The method of claim 1, wherein thefirst substrate comprises a member selected from the group consisting ofSi and GaAs.
 4. The method of claim 1, wherein the base substratecomprises a member selected from the group consisting of group III-Velements, and SiGe.
 5. The method of claim 1, further comprising thesteps of: removing a portion of the base substrate thus obtaining amodified base substrate; and depositing at least one probe pad on themodified base substrate.
 6. The method of claim 5, wherein the quartzsubstrate comprises a first surface and a second surface, the resonatorfurther comprising at least one first electrode on the first surface,and at least one second electrode on the second surface.
 7. The methodof claim 6, wherein the quartz substrate further comprises at least onevia connected to the at least one first electrode and the at least onesecond electrode, wherein the at least one via is filled with a metal.8. The method of claim 7, wherein the quartz substrate further comprisesat least one tuning pad for tuning the quartz substrate to a desiredresonant frequency.
 9. The method of claim 8, wherein the step ofbonding the quartz substrate to the base substrate, comprises the stepof bonding the at least one probe pad to the at least one secondelectrode, thereby allowing a signal to flow between the at least oneprobe pad and the at least one second electrode.
 10. The method of claim8, wherein the at least one tuning pad is ablated to adjust the resonantfrequency.
 11. The method of claim 8, wherein the tuning pad is oneamong the at least one first electrode and the at least one secondelectrode.
 12. The method of claim 1 wherein thinning the quartzsubstrate is performed using a lap and polishing process and reactiveion etching.
 13. The method of claim 12, wherein the lap and polishingprocess uses aluminum oxide.
 14. The method of claim 12, wherein the lapand polishing process uses silica or cerium oxide.
 15. The method ofclaim 12 wherein reactive ion etching uses a gas having a fluorinechemistry.
 16. The method of claim 1 wherein optically monitoringcomprises spectropic ellipsometry.
 17. The method of claim 1 whereinoptically monitoring comprises reflectometry.